1. Field of the Invention
The present invention relates to a process of preparing 2,2'-(1-methyl-1,2-ethanediylidene) bis[hydrazine carboximidamide] having greatly reduced impurities therein useful in a method of treating cancer or advanced malignant diseases.
2. Reported Developments
The compound 2,2'-(1-methyl-1,2-ethanediylidene)bis[hydrazine carboximidamide] is known by several names, such as 1,1'[(methylethanediylidene)dinitrilo] diguamidine, pyruvaldehyde bis (amidinohydrazone), mitoguazone and methylglyoxal bis-guanylhydrazone, methyl GAG or MGBG, represented by the formula ##STR1##
MGBG and its salts have been disclosed in the prior art since the 1950s for use against various diseases as illustrated by the following patents and publications.
The antitumor activity of MGBG in leukemia-L1210- and adenocarcinoma-755-bearing rodents was first reported by Freelander et al, 18 Cancer Res. 360 (1958).
Japanese 51044643 discloses MGBG and its acid addition salts as effective agents against virus diseases of fishes to prevent and treat infections, pancreatic necrosis and hematopoietic necrosis.
Japanese 50029520 discloses MGBG and its salts for use against influenza virus.
U.S. Pat. No. 4,201,788 discloses MGBG for the treatment of non-malignant proliferative skin diseases.
MGBG is known to inhibit S-adenosylmethionine decarboxylase (SAMD), which is a key enzyme in polyamine Synthesis, leading to cellular polyamine depletion. However, investigations with MGBG revealed unacceptable levels of toxicity. The toxicological effects of MGBG observed, some of which are peculiar to certain animal species, include gastrointestinal toxicity, delayed and fatal hypoglycemia, hepatic and renal damage, bone marrow depression, diarrhea and phlebitis. These effects have also prevailed in human subjects undergoing MGBG treatment. Additionally, several toxic effects were demonstrated which are unique to man. These include esophagitis, ulcerative pharyngitis, laryngitis, stomatitis, genital mucosa swelling, conjunctivitis, mucositis, erythema, edema, desquamating dermatitis, and profound anorexia with associated weight loss. Patients who were administered MGBG on a daily schedule exhibited remission to acute leukemia only after a precarious struggle with the oftentimes life threatening side effects. In many patients, treatment had to be discontinued before any beneficial results could be noted.
Knight et al in Can. Treat. Rep., 63 1933-1937 (1979) found that the levels of toxicity were dose schedule related and could be controlled. U.S. Pat. No. 4,520,031 addresses the issue of such does schedule related control in order to reduce toxicity.
The dose schedule control, as described in the patent was based on the postulation that MGBG exerts an inhibitory action relative to polyamine biosynthesis. Physiologically achievable effects of MGBG may be related to the inhibition of the enzyme S-adenosyl methionine decarboxylase, which catalyses the synthesis of the polyamine, spermidine.
Spermidine is believed to play an important role in the initiation of DNA synthesis. Studies have shown that MGBG-mediated depression of DNA synthesis is associated with spermidine depletion and putrescine accumulation.
Another area in which polyamines are believed to play a major role is in RNA synthesis, especially that of transfer (t) RNA. The methylation of tRNA may be directly stimulated by polyamines, a finding of particular interest in light of the reports that neoplastic tissue differs from normal tissue with respect to the extent of methylated tRNA. Here, too, spermidine appears to play a critical role.
Polyamine accumulation appears to be a necessary requisite to DNA synthesis at an optimal rate, in both normal and neoplastic tissues. Thus, the toxicity of MGBG observed in tissues with rapid turnover (skin, G.I. mucosa and bone marrow) may be directly related to inhibition of polyamine biosynthesis and a subsequent depletion of RNA and DNA, the agents which ultimately regulate cell replication. There is, however, strong evidence that: (1) polyamines are excreted in excess in the majority of cancer patients; (2) polyamines, especially spermidine, are released from tumor cells during and after effective chemotherapy, with an initial peak in excretion and in serum levels and subsequent drop toward normal values; and (3) chemotherapy which produces only bone marrow (or other normal tissue) toxicity, and is without antitumor effectiveness, does not produce a significant increase in polyamine excretion. The latter observation would suggest either that cancer cells have much higher levels of polyamines than normal cells, even those with higher rates of DNA synthesis, or that therapy which is effective produces rather specific effects on polyamine synthesis in cancer cells. Thus, the depletion of spermidine is associated with the action of MGBG.
In studies conducted on men, toxicological effects observed clinically have been attributed to cumulative effects of repeated daily doses. This cumulation of accretion of toxicity is possibly explained by the unusually prolonged period required for urinary elimination of MGBG in man. Bioavailability studies in man with MGBG-C.sup.14 have shown that following a single intravenous infusion over a period of 20 minutes, the radioactivity rapidly disappeared from the plasma and that over an extended period of 3 weeks approximately 60 percent of the drug was excreted unchanged in the urine. These data suggest that MGBG accumulates in the tissues and is slowly leached from tissue deposits to accomplish elimination.
The patentee, after considerably large number of studies conducted with MGBG in the treatment of various tumors, concludes that a weekly schedule of administration is most effective in achieving a higher therapeutic index while reducing toxicity to an acceptable level. Accordingly, a dose range of from 250 mg/m.sup.2 to 1000 mg/m.sup.2 of MGBG administered at weekly intervals was established for the treatment of various tumors.
While the above-indicated dose range decreases toxicological side effects and affords treatments of various tumors, long term accumulation of MGBG is still a problem requiring further studies and/or treatment modifications.
Applicants have conducted extensive studies of MGBG with the object to further reduce toxic side effects thereof. In the course of their studies it was discovered that MGBG contains relatively large amounts of impurities which may contribute to the toxicological side effects of MGBG. Accordingly, great efforts were expended to identify and reduce the amount of impurities present in MGBG and its salts.